In the copolymers produced according to this invention the units originating in carbon monoxide and the units originating in the olefinically unsaturated compound(s) used in the preparation occur substantially in an alternating order. Furthermore, the copolymers are regioregular and stereoregular, in particular isotactic.
The term "regioregular" used herein refers to the way in which the units originating in a monomer CH.sub.2 .dbd.CH--R, R being an aliphatic alkyl group, are bound to units originating in carbon monoxide. Three possibilities are distinguishable, which are termed "head/head", "tail/tail" and "head/tail". They may be represented schematically as follows:
head/head: --(CH.sub.2)--(CHR)--(CO)--(CHR)--(CH.sub.2)--
tail/tail: --(CHR)--(CH)--(CO)--(CH.sub.2)--(CHR)--
head/tail: --(CH.sub.2)--(CHR)--(CO)--(CH.sub.2)--(CHR)--
Regioregular copolymer are understood to be copolymers in which the units originating in the monomer CH.sub.2 .dbd.CH--R are bound to the units originating in carbon monoxide predominantly in a head/tail fashion. The degree of regioregularity of such a copolymer is expressed as the average regioregularity, which may be defined as the percentage of the number of units originating in the monomer CH.sub.2 .dbd.CH--R which are bound to the units originating in carbon monoxide in a head/tail fashion.
The term "stereoregular" used herein refers to the configuration of the chiral carbon atoms present in the regioregular copolymer chains relative to the configuration of the chiral carbon atoms together with which they form part of a diad. A diad in this connection is understood to be a segment of the polymer chain which is made up of two chiral carbon atoms which are interconnected through a --(CH.sub.2)--(CO)-- bridge. As regards the relation between the configurations of the two chiral carbon atoms of a diad, two possibilities are distinguishable, which are referred to as "isotactic" and "syndiotactic": when the two chiral carbon atoms in a diad have the same configuration this diad is called an isotactic diad, whereas the diad is called syndiotactic when the configurations are opposed. These options can be schematically represented as ##STR1##
The regioregular copolymers can be divided according to the structure of their chains into three classes:
1) Polymer mixtures in which the number of isotactic diads is substantially equal to the number of syndiotactic diads are referred to as atactic. PA1 2) Polymer mixtures in which the number of isotactic diads is larger than the number of syndiotactic diads are referred to as isotactic. PA1 3) Polymer mixtures in which the number of syndiotactic diads is larger than the number of isotactic diads are referred to as syndiotactic. PA1 a) a palladium compound, PA1 b) an anion of an acid with a pKa of less than 2, and PA1 c) an asymmetric phosphorus bidentate ligand of the general formula R.sup.1 R.sup.2 P--R'--PR.sup.3 R.sup.3, wherein R' is a bivalent bridging group containing at least two carbon atoms in the bridge, and R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are identical or different optionally polar substituted hydrocarbyl groups, such as the (+)-form and the (-)-form of 4,5-bis(diphenylphosphinomethyl)-2,2-dimethyl-1,3-dioxolane and (-)-4,5-bis(dibutylphosphinomethyl)-2,2-dimethyl-1,3-dioxolane.
The atactic polymer mixtures mentioned under 1) are stereoirregular, whereas the other regioregular polymer mixtures mentioned above possess a degree of stereoregularity. The degree of stereoregularity of the isotactic polymer mixtures is expressed as the average stereoregularity or isotacticity, which is understood to be the percentage of isotactic diads, calculated on the total number of diads present in the polymer chains. On the basis of this definition, the isotactic polymer mixtures have an average stereoregularity of more than 50%.
EP-A-384517 and EP-A-410543 disclose copolymers of carbon monoxide with an aliphatic -olefin having at least three carbon atoms which are made up of linear chains in which the units originating in carbon monoxide alternate with the units originating in the -olefin. These copolymers have a certain degree of regio- and stereoregularity, more specifically they are isotactic in nature. For the sake of simplicity the polymer mixtures may be described as isotactic linear alternating copolymers. EP-A-385517 discloses that the copolymers in question can be prepared by contacting a mixture of the monomers with a catalyst composition comprising
In Macromolecules 25, 3604-3606 (1992) it is taught that by using as the asymmetric ligand (6,6'-dimethylbiphenyl-2,2'-diyl)bis(dicyclohexylphosphine)an isotactic linear alternating carbon monoxide/propene copolymer can be prepared which has an isotacticity of about 88%, as calculated from the .sup.13 C-NMR data provided.
EP-A-410543 teaches that when isotactic copolymers are prepared which have a lower degree of isotacticity than required for a certain application, they can be treated to increase their degree of isotacticity, e.g., by extracting the copolymers with a suitable solvent. It is disadvantageous that in this treatment a polymer byproduct is obtained which in many cases has to be discarded because it does not fulfil the requirements as regards tacticity. It would therefore be desirable to modify the polymerisation such that copolymers with a high degree of isotacticity can be prepared efficiently, i.e. such that the treatment can be avoided and also that the rate of polymerisation is improved.